Material processing with lasers has been well known in the area of heat treatment, welding, cutting and drilling. Such applications typically involve the imaging of the emitted laser beam into a small focus area at a sufficient intensity required by the particular application. For focussing, generally optics are used which may be of the simple spherical, cylindrical or of the most recent binary/refractive types.
These types of classical optics are generally limited to imaging the cross-sectional intensity of the incident laser beam into a smaller or larger focus. Thus a round laser beam is limited to drilling round holes without further manipulation of the workpiece. The binary/refractive optics have circumvented some of the imaging limitations by being able to transform simple cross-sectional intensity profiles into other simple cross-sectional profiles, such as, disk to ring, Gaussian to top hat, etc.
In the area of welding, the classical weld joints, such as, butt, lap, etc., can be now accomplished with a laser. The weld itself can be made autogenously or with the addition of material into the weld seam. The added material typically is in the form of a powder for lasers and wire for other welding technologies. Because the laser is typically delivered to the workpiece via a numerically controlled machine tool, the working process is readily automated.
In one of the areas of application involving aircraft engine turbine components, when material is added to a narrow, curving geometry of a workpiece, it is critical to deliver the proper amount of energy at a proper translation speed of the workpiece and/or the laser focus. The laser focus itself must be accurately aligned to the individual component of the workpiece, which typically requires that the laser focus path be individually programmed for each component. Also, attempts have been made to focus the laser beam onto the workpiece by an optical system involving mirrors. It is well known that a mirror can be used for prefocussing or reflection, however, when a mirror is used to focus a high intensity beam, it is susceptible to frequent damage due to the close proximity of the actual laser processing location. Such additional manufacturing steps make the use of such known technology time consuming, costly and prone to errors.
Such shortcomings of laser beam imaging and focussing appear to have been overcome in some limited areas of manufacturing, such as demonstrated by U.S. Pat. No. 3,617,702 issued Nov. 2, 1971 to Philip Flournoy and entitled Apparatus and Method for Perforating Sheet Material, wherein a reflective holographic optical element (HOE) is used for imaging hole-like patterns onto a moving plastic sheet material and perforating the plastic material where such images impinge thereon. The teaching of this patent is specifically intended to be incorporated herein by reference for enabling one skilled in the art to understand the present invention without the disclosure of extraneous material.
It has been known that HOEs inherent in their method of making can be classified as transmissive or reflective HOEs. The making of such reflective HOE and its use in a relatively low-power application has been described in the referenced patent. It is also known that most high power lasers are at infrared wavelengths between 1 and 10 micrometers. There are no known photoemulsions which would be of sufficient resolution and sensitivity to record a HOE in the infrared spectrum.